Electron emitting element for electron gun



TRQE- S? 4, xR 'gnw ggg y 2?, 1965 .1. L. SQLOMON 3,197,569

ELECTRON EMITTING ELEMENT FOR ELECTRON GUN Original Filed Mai; 12, 1961 5 Sheets-Sheet l 5%- .Jizaerg/ar UL'i U5 1., SOL 0 MON July 27, 1965 J. L. SOLOMON ELECTRON EMITTING ELEMENT FOR ELECTRON GUN Original Filed May 12,

3 Sheets-Sheet 2 July 27, 1965 J. L. SOLOMON 3,197,669

ELECTRON EMITTING ELEMENT FDR ELECTRON GUN Original Filed May 12, 1961 3 Sheets-Sheet 5 i 720624502". J'uL/us L, SOLOMON United rates Patent G 3,197,689 ELECTRGN EMETHNG ELEMENT FDR ELECTRON GUN Julius Lee Solomon, Chicago, lli., assignor to Welding Research, inc, tlhicago, ill, a corporation of Illinois Originai appiication May 12, 1961, Ser. No. 109,575, new

Patent No. 3,187,216, dated June 1, 1965. Divided and this application May 23, 1961, Ser. No. 112,984

2 Claims. (Cl. 313-342) The invention relates to an electron beam gun and has reference more particularly to a new and improved electron emitting filament ior an electron gun which will be mechanically and electrically stable.

This application is a division of a copending application of David Sciaky, Serial No. 109,575, filed May 12,

1961, entitled Electron Gun now Patent No. 3,187,216

issued June 1, 1965. I

When devices of the character as described are used for welding, the stream of electrons is accelerated and focused by structure designed for the purpose whereby a high power density beam is produced for impinging on the work pieces, with the result that the energy of the beam is transferred to the work to cause fusion. The essential elements of such a welding device comprise a supporting body portion, a filament, a cathode, an anode and a focusing coil. The elements are so designated and have such correlation with each other that various metals and particularly those characterized by a high melting temperature can be satisfactorily welded within a vacuum.

An object of the present invention is to provide a fila ment for such an electron gun which will be inexpensive to produce, which will be highly efiicient in operation, and which will have a shape such as to materially facilitate easy insertion and removal of the filament from the clamping means of the gun.

Other objects of the invention are to provide a new and-improved filament for an electron gun that can be punched from a metal plate, thus making possible reproductions which will be accurate as to shape and dimensions; to provide filaments for an electron gun wherein the area for electron emission will be precisely the same for each filament; and to provide filaments for the purposes as stated which will be sturdy and mechanically and electrically stable.

Another object of the invention is to provide a filament for an electron gun which will be made of tantalum or other suitable materials, which will be precisely shaped to provide a flat emitting surface, and wherein the shape of the filament will be such that the magnetic field caused by the flow of current, and thus the dispersion of the electron beam as caused by the magnetic field, will be substantially eliminated.

With these and various other objects in view, the invention may consist of certain novel features of construction and operation, as will be more fully described and particularly pointed out in the specification, drawings and claims appended thereto.

in the drawings which illustrate an embodiment of the device and wherein like reference characters are used to designate like parts FIGURE 1 is a longitudinal sectional view taken substantially along line 11 of FIGURE 2, and which shows the structural details of an electron gun incorporating the improved filament of the invention;

FIGURE 2 is a top plan view of the electron beam gun of FIGURE 1;

FIGURE 3 is a fragmentary sectional view similar to FIGURE 1 but which more clearly illustrates the mode of operation of the electron gun as disclosed;

FIGURE 4 is another fragmentary sectional view illustrating the adjustable clamping means forthe spacing rings;

FIGURE 5 is still another fragmentary sectional view and which shows in detail the manner in which the present filament can be releasably clamped to the current conducting electrodes of the gun; FIGURE 6 is a plan view of the filament in clamped arrangement as shown in FIGURE 5;

FIGURE 7 is adetail view showing the size and shape of the metal blank prior to the bending thereof for forming the filament; and

FIGURE 8 is a schematic view showing electrical connections for the various elements of the electron beam gun as disclosed.

Referring to the drawings and in particular to FIG- URES l and 2 the embodiment selected for illustrating the invention employes a cap or body portion 26 from which the various parts of the gun are suspended. The said body portion is formed of insulating material having good dielectric strength, good heat conductivity, and which is also mechanically strong with low moisture and gas absorption. The body portion accordingly suspends a pair of electrodes 22 and 24 for conducting current to the filament 25. The body portion also suspends a spaced inside shell or cage 26 for supporting the cathode 27 and a spaced outside shell or cage 28 which functions as a holder for the anode 30.

The current conducting electrodes 22 and 24, and the inner cage 26 comprise a unit which is supported from the insulating body portion 29 primarily by the plate members 31 spaced and insulated from each other and to which the cage 26 of stainless steel is welded as at 32. The plate members 31 are secured centrally to the body portion and this central section is cored to provide the elliptical opening 33, FlGURE 2. Said opening receives the sockets 34 and 35 preferably formed or" copper and which have a plug receiving recess 35 in their exposed top end whereas their reduced depending end is threaded at 37. This end of each socket extends through a washer of insulating material such as 33 and through its respective plate member 31 and the end is threaded into one of the electrodes. Thus socket 34 is mechanically and electrically connected to electrode 22, whereas socket 35 connects with electrode 24. The sockets 34 and 35 are adapted to receive plugs, not shown, and which electrically connect the sockets and thus the electrodes to a source or" current for heating the electron emitting filament 25. Said sources of current may have a voltage of about 5 volts with an amperage which may average approximately 40 amperes.

The electrodes 22 and 24 are thus disposed in a depending, side by side relation relatively adjacent each other and which requires the location-of spacers of insulating material such as 40, 41 and 42 for maintaining the electrodes in desired spaced relation. Thesecuring bolts 43 extend through the electrodes and through the washers 41 and 42, respectively, to receive the nuts 44 and which are properly insulated from electrode 22. The electrodes are thus mechanically connected to form a unit and which support on respective sides a clamping arrangement for clamping the filament to the electrodes. Each electrode has a clamping bar such as 45 and 45 disposed in contact with its outside surface and each bar provides a lower flange 47 and 48 adapted to contact a shoulder such as St) on its respective electrode. A clamping member 51 is provided for each bar and the same contacts its bar at longitudinally spaced locations for which purpose each member 51 is provided with feet 52. A bolt 53 extends through each of the members and through its associated clamping bar and has threaded connection with its respective electrode. The clamping members are preferably formed of metal such as copper and which has some resiliency since upon tightening the bolts 53 it will be understood that a spring loading action is applied to each clamping bar, thus forcing and securely maintaining the flanges 47 and 4-3 against a shoulder to thus provide a good mechanical and electrical clamp for the lilament 25.

The inner cage 25 of substantially cylindrical shape may be constructed of stainless steel and the cage is formed with a plurality of openings 49 whereby convenient access is provided for manipulating the screws 52. Release of the screws and disassembly of the clamping arrangement will be necessary in the event a filament has to be replaced.

The lower terminal end of the inside cage 26 is threaded as at 54 and this threaded end receives the retaining ring 55 for releasably retaining the cathode 27 in place on the bottom of the cage. The said cathode is maintained at a negative potential of approximately 50,000 volts and the same is provided with a center opening which receives the axially positioned filament It is important that the filament have an accurately aligned relation with the opening for the most etficient production of electrons and also the undersurface of the cathode 27 is shaped at 56 as best shown in FIGURE 3 for the same purpose.

The filament 25 is formed from a strip of metal 58, FIGURE '7, such as tantalum or tungsten, the same having a shape as shown in FIGURE 7. The relatively wide extremities 59 comprise the portions of the same which are clamped between the shoulders 54 and the flanges 47 and 48, respectively. The connecting portions 60 narrow the strip down to a central section 61 and which has a length whereby to permit a bending of the section back on itself while still presenting a surface area adequate for the emission of electrons for the present gun. With the filament in clamped engagement with the electrodes 22 and 24 as shown in FIGURE 5 the connecting portions 60 extend diagonally downward and inward to thebends 52 whereupon the metal strip extends laterally outward to the outside bends 63.

The formation of the filament 25 as described and as shown in FIGURES l, 3 and 5 has the desirable effect of reversing current flow with respect to the central emitting section 61 and thus the magnetic field caused by flow in one direction is nullified by current llow in an opposite direction and vice versa. The magnetic field which would otherwise exist is eliminated and thus dispersion of the electron beam as would be caused by such a magnetic field is also eliminated. in other words, the formation of the filament by its non-inductive nature minimizes the magnetic field produced by the filament.

The electron beam should emerge vertically from the gun and in this respect the filament is important. Its flat area provides an electron emitting surface of definite size and which can be maintained fiat or as an alternative the entire filament can be replaced at relatively little expense and in a most easy and rapid manner. Since the filament is accurately reproducible a change in filament does not interfere in any manner with the operation of the apparatus.

The shape of the filament is such as to locate the clamping portions in planes which are at right angles to the ilat area. Also, the metal of the strip at each end of the flat area has the reverse bends 62 and 63 which elfect a reversal in current flow all as described, and further the width of the filament in this area is a mini mum.

The outside shell or cage 28 is likewise provided with a plurality of openings 65 and the said cage is suspended from the body portion 20 by the encircling clamp 66. The cage at its upper end is welded at 67 to the clamp and which is held to the body portion by the securing bolts 68 being located under the annular flange 69 which comprises an integral part of the body portion. The cage provides a support for the ring 73 of insulating material having the same desirable characteristics as the material of the body portion. The anode 30 is supported and accurately positioned by the ring 70 with its opening '71 in alignment with the opening in the cathode 27 and with the filament 25. The anode is given a positive potential and for the most satisfactory results in operation it is preferred to make the anode of tantalum. Since the spacing of the anode 30 from the cathode 27 determines the power ratings for the present electron gun, that is the maximum value of beam current at maximum Voltage, the invention provides adjustable hangers 72 and spacing rings such as 73, FIGURE 3, for varying the cathode-anode distance. Two hangers 72 are provided diametrically spaced on the cage 23 and each hanger is slotted at 74 and formed with a groove 75 at its depending end. An annular flange 76 on the anode supporting ring 70 is retained by the groove 75 and a threaded stud 77 extends from the cage through the slot 74 and re eeives the releasable knob 73.

in FIGURE 1 the anode supporting ring 70 and thus the anode 34B are spaced the minimum distance from the cathode to give the maximum rating for the gun, for example 300 milliamperes at maximum operating voltage of about 25,000 volts. Since lower currents at the maximum voltage are often desirable, spacing rings are employed and which are interposed between the end of the cage 28 and the ring 70. For example, in FIGURE 3, the ring 73 lowers the anode 39 to an extent which gives a current of approximately 50 milliamperes. In FIG- URE 4 the ring '89 is greater in length and thus the cathode-anode distance is increased for a relatively low current of about 25 milliamperes.

Below the annular flange 69 the body portion 20 is formed with :1 depending nose portion 81 and which presents an inwardly sloping surface 32 extcriorly of the body portion and a relatively long surface within the body portion until the inside cage 26 is reached. In accordance with the invention the nose 81 is interposed between the inside and outside cages 26 and 28, respectively, to present the maximum creep distance between these parts. This is desirable since the parts have a high potential difference during operation. The result of this structure is to insure safe operation of the gun at said high operating potentials and without any arcing.

For focusing and directing the electron beam so as to direct a beam of maximum density for welding the work piece, a focusing coil 83 is suspended by the screws 74 from the anode supporting ring 70. The said focusing coil essentially consists of a pair of coils such as 84 and 35 encased in an enclosing shell 36 of iron and which have an armature 87 also of iron located between the adjacent inner edges of the coils. An air gap 88 exists on each side of the armature between the same and the interior cylinder of iron 90 for the respective coils. The air gaps are thus located at the central plane of the focusing coil. A relatively low voltage, direct current is caused to flow through the coils 34 and to provide a magnetic effect within the central passage formed by the interior cylinders 90. The focusing coil is located below the anode where the electron beam starts to diverge. The action of the magnetic flux from coil to armature is such as to cause the beam to converge and by adjusting the current fiowing in the coils the beam of electrons can natural phenomenon by providing the, focusing coil 33.

enemas The coil is located a predetermined distance below the anode 39 and even though different spacing rings are used, this distance remains fixed.

The electrical circuit for the gun is shown schematically in FIGURE 8. The alternating power supply indicated by the leads L and L includes the primary winding 96 of a transformer 97 which has a secondary winding 98 connected to the conductors 100 and 101, which in turn supply a heating current at the desired voltage to the electrodes 22 and 24, and thus to the filament 25. The high voltage power supply furnishes a direct current at the desired voltage for maintaining the required electrical field between the cathode and the anode. The negative conductor 192 is connected to the conductor 16%) and the conductor 103 completes the circuit to the cathode 27. The positive conductor 104 from the high voltage power supply has connection with the anode 30 and a parallel circuit including conductor 165 is connected to the workpiece and grounded.

It is to be understood that the invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings, as various other forms of the device will, of course, be apparent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. An electron emitting element comprising a strip of metal of substantially the same thickness throughout but which varies in width, said element having a shape providing a pair of spaced clamping portions, a centrally located uninterrupted fiat area and diagonal portions connecting the clamping portions with the flat area, said clamping portions being disposed in parallel planes and which have a right angle relation with the flat area, said flat area at respective ends being joined to the diagonal connecting portions by the metal of the strip and which has reverse bends, whereby the magnetic field such as may be caused by current flow in the fiat area is substantially nullified, and the said strip having its maximum width at the clamping portions and its minimum width along the length of the flat area.

2. An electron emitting element comprising a strip of metal of substantially the same thickness throughout but which varies in width, said element having a shape providing a pair of spaced clamping portions, a centrally located uninterrupted fiat area and diagonal portions connecting the clamping portions with the flat area, said clamping portions being disposed in parallel planes and which have a right angle relation with the flat area, the said strip having its maximum width at the clamping portions and its minimum width along the length of the flat area, and the electron emitting element having a noninductive shape which minimizes the magnetic field produced by current flow in the metal strip.

References Cited by the Examiner UNITED STATES PATENTS 2,111,940 3/38 Schlesinger 313-342 X 2,283,896 5/42 Mouromtseif et al 313-342 2,727,177 12/55 Daily et a]. 313341 3,034,012 5/62 Gasson 3l3-34l X 3,069,584 12/62 Frazer 313-311 X GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. 

1. AN ELECTRON EMITTING ELEMENT COMPRISING A STRIP OF METAL OF SUBSTANTIALLY THE SAME THICKNESS THROUGHOUT BUT WHICH VARIES IN WIDTH, SAID ELEMENT HAVING A SHAPE PROVIDING A PAIR OF SPACED CLAMPING PORTIONS, A CENTRALLY LOCATED UNINTERRUPTED FLAT AREA AND DIAGONAL PORTIONS CONNECTING THE CLAMPING PORTIONS WITH THE FLAT AREA, SAID CLAMPING PORTIONS BEING DISPOSED IN PARALLEL PLANES AND WHICH HAVE A RIGHT ANGLE RELATION WITH THE FLAT AREA, SAID FLAT AREA AT RESPECTIVE ENDS BEING JOINED TO THE DIAGONAL CONNECTING PORTIONS BY THE METAL OF THE STRIP AND WHICH HAS REVERSE BENDS, WHEREBY THE MAGNETIC FIELD SUCH AS MAY BE CAUSED BY CURRENT FLOW IN THE FLAT AREA IS SUBSTANTIALLY NULLIFIED, AND THE SAID STRIP HAVING ITS MAXIMUM WIDTH AT THE CLAMPING PORTIONS AND ITS MINIMUM WIDTH ALONG THE LENGTH OF THE FLAT AREA. 